The Titus Tunnel, Turkeysupposedly built in the Roman periods, but probably not at all because its style belongs to a completely different older periods (plus there are ruins in that old style in the vicinity)

Longyou Grottoes, Chinathe machine tool marks are clearly visible, the complex is so large that the full mountain is practically hollow

Orvieto, Italythe older parts show signs of identical extreme age and identical design elements like that underground cities of Cappadocia, subsequently used and remodelled by later cultures (as everywhere else, again)

Kanheri caves , Indiaalthough the bas-relief are splendid, what is even more interesting is the fact that caves were carved in already existing older complex of caves, one belonging to the worldwide network of such underground dwellings...